I was joining the M27 motorway one afternoon when I noticed a Vauxhall in my rearview mirror shifting pretty fast in the outer lane. The car overtook me at some speed and tried to force his way into the first lane and beyond. In front of me was a Fiat 500 and a 4 x 4 towing a trailer at a very slow speed so I had to back off. The Vauxhall forced his way into lane 2. Another car in lane 2 and behind had to brake hard and change lanes a bit sharpish. That car was now in 3rd lane and moved over back into lane 2. The Vauxhall indicated to overtake him and then he moved into lane 3 blocking the Vauxhall. He then brake tested the Vauxhall by slamming his brakes on. All in all a scary situation not only for me but also the slow moving traffic in front. Luckilly there was no colision and the Vauxhall driver thought better of 'racing' and seemed to calm down although he stayed in the 2nd lane hogging for about another mile or so until I exited at the next junction.